[ba] Coupe stopping intermittently,

Ti Kan ti at amb.org
Mon May 17 16:07:35 EDT 2004

audion at serversmiths.com writes:
> Well, I tested everything pretty thoroughly and either have a defective 
> new relay (@ $60+) or the coil is not putting out enough voltage to 
> trigger the circuit (which I doubt). I measured about .7 to .8 of a 
> volt coming off the coil connector going through the relay to ground 
> although it "seems" to show the full 12V+ of the system for a second 
> and then drop to the .7 - .8 volts.

Without looking at how your fuel pump relay is hooked up I can't
comment on why it's not working, but you can't just measure the
ignition signal with a voltmeter and expect to get a reasonable
reading.  This is something more appropriately done with an

> Using a standard Bosch relay outboard of the relay panel gets 12V to 
> the pump and the car runs fine. So, I'm inclined to cut my losses time 
> and money-wise and try and rig up an alternate safety feature to shut 
> off the pump if the engine is not running.

Not a great idea.  You should double check your wiring.

> What are the other methods used by car makers to shut off the fuel pump 
> if the engine is not firing? Is it always a signal from the coil to a 
> custom fuel pump relay?

For Bosch CIS injection, the Audi way is the Bosch way, and was also used
on VW, Saab, Volvo, Mercedes, ... even Ferrari.  Of course later cars
became more sophisticated, with ignition and fuel control all in a single
ECU, so the ECU itself does the job.

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